In glycoconjugate biosynthesis, sialyltransferase plays an essential role in catalyzing the addition of termimal sialic acid to a variety of acceptors. Elevations of circulating sialytransferase have been reported in patients with malignant disease. Our earlier reports stongly indicate that sialyltransferase may indeed by a reliable biomarker for breast cancer. Recent investigations in our laboratory further suggest that there is a correlation between tumor sialyltransferase and the degree of metastasis to axillary lymph nodes in women with primary operable breast cancer. Thus, sialyltransferase appears to show significant clinical potential for use as both a diagnostic and prognostic tool and we propose to develop a reliable clinical solid phase immunoassay system using the monoclonal antibody technolocy. We also propose to investigate whether there is any correlation of cell surface sialic acid and sialyltransferase with the metastasizing capacity of human breast tumors. Such studies are essential because the metastatic potential of malignant cells rests on their surfaces and also because of the possible role of sialic acid and sialyltransferase in intracellular recognition and adhesion. Our studies will also focus on the important issue of the origin of elevated levels of circulating sialyltransferase in breast cancer patients. The studies will include the purification of serum, mammary tumor and liver sialyltransferases by immunoadsorption techniques and comparison by biochemical and kinetic parameters. A study of isoenzyme patterns of sialyltransferase from various sources will also be conducted.